Recently, I noticed the tendency of students to squeeze out small bits of paint for a class. Painting when you don't have enough paint affects your whole attitude toward the work. It says "I'm probably not going to make a good painting so why waste good paint." That's a poor position from which to start anything. If you want to progress, then as a student, it's your job to use enough paint to learn. Some may say cost is an issue but I think if you look at the bigger picture, the cost of hampered learning is much higher. Learning to paint can be frustrating. But some frustrations are easily fixed with good brushes and enough paint.
Sometimes you won't use all the paint you put out. Nothing is more annoying then when I put out paint and don't use it. It gets a skin and it's done. If you feel this too, then get your palette knife and some old support. Make a simple study from palette scrapings. It's fun and instructive! Don't worry over it, don't do a drawing under it. Just practice mixing the right color, value and shape. Place them in their relative proportions. The more you paint, the more you learn!
Below is a small (8x10) palette knife study done with palette scrapings. Try it.
This idea is not mine, I read it in a Richard Schmid book years ago. Thank you, Richard